1. Field of the Invention
The present invention relates to a developing device in an image forming apparatus, which develop an electrostatic latent image on a photosensitive body by a developing roller.
2. Description of the Related Art
In conventional image forming apparatus such as an electrophotographic copying machine, a magnetic brush developing device is used. The magnetic brush developing device develops the electrostatic latent image on the photosensitive body using a magnetic brush with uniform tufts formed on a developing roller. The developing roller comprises a magnet and a cylindrical sleeve. Alternatively, such apparatus used a developing device which developed the electrostatic latent image by a non-magnetic one-component developing agent which electrostatically adhered to a non-magnetic developing roller. In order to obtain a developed image with a constant density, cylindrical gap rollers were provided on both sides of the developing roller as described in Japanese Laid-Open Patent (Kokai) No. HI-93774. The gap between the surface of the photosensitive body and the developing roller was kept uniform by pressing these gap rollers on the non-image formation region of the photosensitive body.
In the conventional image forming apparatus, the gap rollers for maintaining a uniform gap between the surface of the photosensitive body and the surface of the developing roller were pressed under constant load on the non-image formation regions of the photosensitive body by springs or by the weight of the developing device itself. For this reason, highly accurate gap rollers were required for obtaining an image with stable and uniform density. Despite this, and although the gap rollers were not easily distorted and used materials with minimum distortion, because of the construction, the gap rollers were liable to undergo uneven loads in the stationary state during non-developing operation, which resulted in distortion. Thus, there was the problem of the occurrence of density randomness due to the distortion of the gap rollers, leading to a great reduction of picture quality. At the same time, when the developing device was installed against the photosensitive body, if the pressure of the gap rollers on the photosensitive body was too great, this pressure caused a resistance which interfered with rotation of the photosensitive body during the developing operation, leading to randomness in the rotation of the photosensitive body. Therefore there was also the problem a great reduction of picture quality due to image blurring.